Optimax economy question

[640 blazer]

I have a 21ft fibreglass 22deg dead rise delta pad hull with hard top weighing 2 tonne off the trailer powered by a 200hp Optimax , It averages 1 statute mile per lt . My question to anyone who may know is is this fuel burn good bad or average ? I have had the boat 7 years it is my first so am interested to know .

[TollyWally]

I'm an inboard guy but it doesn't sound too bad. I get 1.5 knts/gallon weighing in at about 8000# I'm sure a few guys with similar situations will weigh in with better data.

You guys are midway through spring right now aren't you? My favorite time of the year, with all of summer ahead of you. Enjoy!

[Willallison]

1 litre per statute mile is equvalent to about 4.5 statute mpg, or just under 4 nautical mpg. That's very good for a big, quite heavy deep-v hull. Most would use about twice that (TollyWally being one!)
Opti's are generally pretty miserly - these days there's little to choos between direct injection 2-strokes and their equivalent 4-strokes.

[tom28571]

I looked at that 4.5mpg and thought, whoah there. then I remembered gallons were bigger down under. That would be 3.8 mpg on Fox Island. Still very good for a deep V.

[Willallison]

yes - sorry, probably should have said imperial nautical mile per gallon....

[marshmat]

640blazer, your numbers do look reasonably good for a hull of that configuration and weight. Optimax motors are rather heavily computerized, and all those sensors and processors do seem to pay off in somewhat lower than average fuel burn in many cases. If the boat was new when you got it, that'd be a 2001 motor which, with the Mercury reputation, should run for a while yet. Where you may run into difficulty is in finding replacement parts for it in five or ten years; you certainly wouldn't see much of a fuel economy gain by upgrading now.

If you do want to try improving your fuel economy, and can buy or borrow a fuel flow meter, it's fairly simple to record fuel flow versus speed in various wave/wind conditions, convert to litres/naut.mile (or whatever), and find your most efficient speeds. (Most deep-V boats will have two 'ideal' speeds, one near idle and one somewhere between 20-40 mph, separated by an enormous hump in the 10-20 mph range where fuel consumption skyrockets.)

Without the meter, you can make a remarkably good guess by checking the height of your wake at successively higher speeds. As the boat levels out onto plane, the wake will seem to flatten out a bit; there will be a point somewhere before you feel like you're 'pushing' the engine where the wake is uniform and relatively small, and this point tends to very nearly coincide with minimal fuel consumption. After all, a large chunk of that fuel is being used to force water out of your way into the wake, so a lower wake translates to a more efficient use of your fuel.

[640 blazer]

Thank you for your reply , many of my friends have commented on my fuel burn when going away with several other boats . Yes I did buy the boat and motor new and at the time the toss up was between an Opti or EFI price being the issue but at the time was a single man so couldnt afford not to go Opti , Range was my thinking and range is what I got , the boat has a 216lt under floor tank and hasnt let me down yet on many 170 to 200 stat mile journies although 170 or so miles most common as I do like the idea of reserve . The boat was very light when I fist bought it as it had no hard top small anchor just plain empty I guess compared to now . Maybe its economy comes at a small price as it is a very beamy boat giving it a great deal of room for a 21 footer inside largish spray rails so it is a little hard riding in some conditions but not over the top as I go out in them all . When ever I can sit at speed 95 percent of that time would be at 32 stat mph , the reason I have everything set up in stat miles is beecause it does exactly 1 stat per 1 lt and just for your interest 275ml of oil per hour average over 7 years . Just another point of interest when I bought the boat it had a 19 inch vengance and 56 mph top end , after the weight was poured on over the years it didnt take long to realise it was slowing down and now over proped so went to 17 inertia , 48 tops average rpm up NO EXTRA FUEL BURN .

[Willallison]

Matt - there shouldn't be any need to get a fuel flow meter - the multi-function Optimax gauge will give that info at the push of a button. I'd almost guarantee though that the best economy would be yielded at 4000 rpm. I'm yet to come across a 2-stroke outboard powered rig where this isn't the case.

[640 blazer]

Yes you are correct 3900 rpm is most common for me and yes I have all the typical Opti gauges and figures and just to let you know that the fuel used reads 11 percent low and always has done , I have inquired about having it recalibrated only to be told that cant be done , is this the case ? For the last 7 years I have always filled my tank reset both gps and Opti trip metres then when need be filled tank again and its a simple calculation to come up with a figure , I have been doing this for 580hrs that I have clocked up and fingers crossed that black thing gives me plenty more . And just for the sake of it after 580 hrs havnt seen one puff of smoke , everytime I have turned that key hot cold not run for 3 month , BANG lights up and sits there not missing a beat . You know what they say about going black !

[Willallison]

You'll get no argument from me - we've 2 x 225's and love 'em. Mind you, it wasn't without it's teething problems - one of the powerheads was replaced twice during the running in process!! 1st time a merc tech decided to leave a bolt rattling around inside the motor somewhere during assembly, the 2nd time the computer decided to switch off the oil supply.....
Since then, however, they've never missed a beat. If money were no object, I'd swap them for a pair of Verado's. There's only one thing better than black - and that's younger black!!